The invention relates to a process for connection of electrical loads to the terminals of an amplifier, and for detection of a possible defect of a connection of said electrical loads. It includes an amplification circuit using this process for connection and detection.
Existing automotive vehicles are conventionally provided with an access control device called a “hands free” and with several systems for surveillance and/or measurement of parameters, comprising detectors mounted on said vehicle, each of these monitoring devices and surveillance systems being provided with a low frequency emitter/receiver circuit having an antenna.
Conventionally, and as shown in FIG. 1, the antennas such as A1, A1 of these monitoring devices and surveillance systems are integrated in an amplification circuit comprising an amplifier Am, and are connected to the connection terminals such as B1, B2, B3 of this amplifier Am, as a function of their power:                either according to a complete bridge arrangement adapted to control again the “high” power antennas and consisting in connecting each of the poles of the antenna A1 to one of the terminals B1, B2 by means of an electrical connection branch P1, P2 having for example, according to FIG. 1, either a resistance R1 in series with a capacitance C1 (branch P1), or a resistance R2 alone (branch (P2)        or according to a half-bridge mounting adapted for the control of “low” power antennas, and consisting in connecting one of the poles of the antenna A2 to ground, and the other pole of this antenna A2 to a connection terminal B3 by means of an electrical connection branch P3 having for example a resistance R3 in series with a capacitance C2.        
The principal advantage of such amplification circuits resides in the fact that they promote detecting a possible defect of connection of an antenna A1 or A2, and localizing the defective antenna.
On the other hand, such amplification circuits require a connection terminal B1–B3 for the connection of each of the electrical connection branches P1–P3 (hence three terminals for two antennas), and are thus costly in terms of investment in the amplifiers.
So as to overcome this last drawback, a present solution, shown in FIG. 2, consists in mounting two antennas A3, A4 in parallel between two electrical connection branches P4, P5 of a complete bridge mounting.
According to this principle, two antennas can be connected to an amplifier Am provided with two connection terminals B1, B2, such that an economy in terms of investment (there is saved a connection terminal on the amplifier Am) is enjoyed relative to the solution described in the first instance above.
However, this economy of investment is enjoyed at the detriment of the diagnostic function of the amplification circuit: an amplification circuit according to this second principle permits in effect detecting a possible connection defect, but does not permit distinguishing which of the two antennas A3, A4 is disconnected, and this no matter what the power, absolute or relative, of said antennas.